1. Field of the Invention
The present invention relates to ratchet heads and, in particular, to power-operated ratchet heads and, more specifically, to selector knobs for controlling the direction of operation of the ratchet mechanism.
2. Description of the Prior Art
Reversible ratchet heads are provided with a reversing knob or lever which is typically rotatable between forward and reverse positions to control the direction of rotation of the ratchet mechanism. Typically, the reversing knob is a metal member having a cylindrical shank with an enlarged head, the knob being rotatable about the axis of the shank to effect the direction-reversing function. The ratchet mechanism could be used in either a hand-operated or a power driven device. One such power driven device is an air ratchet tool sold by Snap-on Tools Corporation under Model No. FAR72B.
It has been found that in such prior ratcheting devices, particularly in power driven devices, the reversing knob has a tendency to self-reverse and/or self-lock under certain operating conditions. One such condition is during the rapid rundown of a loose fastener. In this mode of operation the drive body assembly of the ratchet head is torquing at a high rate of speed. The sudden stoppage caused by the fastener bottoming out causes rapid deceleration. The drive body comes to rest due to a drag brake acting on the drive body. However, because of its relatively high inertia, the large-head selector knob has a tendency to keep turning, moving to its other position and reversing the direction of operation of the ratchet mechanism.
Also, when the ratchet device is being used in a hand ratcheting mode, such as for loosening a fastener with a long extension, the sudden loosening or release of the fastener causes a rapid acceleration. Again, the inertia of the reversing knob tends to result in a relative movement between it and the drive body, which can result in self-reversal.
Many ratcheting devices, such as the Snap-on Tools FAR72B, described above, utilize two pawls. During self-reversal, if both pawls change direction, the ratchet mechanism reverses its direction of operation, but if only one pawl reverses its position, a self-locking condition results.
At least one prior art device has attempted to alleviate this self-reversing and/or self-locking tendency by reducing the size of the reversing selector knob. However, in order to overcome the self-reversing problem it has been found necessary to make the selector knob so small that manual operation becomes very difficult. Indeed, in certain such devices use of a needle nose pliers is required to effect manual operation of the selector knob. Other devices have attempted to address the problem by utilizing a latching-type selector knob which must be axially depressed before it can be rotated. Such an arrangement requires the use of additional parts and it is expensive to manufacture and complex to assemble.